Of course, the patent examiner would almost definitely not see the post in their shallow searches for prior art. The patent would get issued, and then it would cost near to the tune of $1million to invalidate it using the court system. Yay patents.
In the UK it's free to submit prior art (S21 of the CDPA I think) to the patent office and IIRC also free to request the office re-examine a patent.
There are better places than HN to submit a defensive publication but HN posts aren't outside the locus of prior art searches unless they get delisted from Google.
Of course it doesn't matter for a competitor what the granted patent says, if they have date verified disclosure prior to the priority date of the granted patent then they can submit that to the court and win a case by invalidating the granted patent.
